Nitrogen oxide reduction catalyst regenerable at low temperature

ABSTRACT

Provided is a nitrogen oxide (NOX) reduction catalyst including an active site including at least one of a metal vanadate expressed by [Chemical Formula 1] and a metal vanadate expressed by [Chemical Formula 2], and a support for loading the active site thereon.(M1)XV2OX+5  [Chemical Formula 1](where M1 denotes one selected from among manganese (Mn), cobalt (Co), and nickel (Ni), and X denotes a real number having a value between 1 and 3.)(M2)YVO4  [Chemical Formula 2](where M2 denotes one selected from among lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu), and Y denotes a real number having a value between 0.5 and 1.5).

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2019-0001371, filed on Jan. 4, 2019, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND 1. Field

The present invention relates to a nitrogen oxide (NO_(X)) reduction catalyst and, more particularly, to a heterogeneous catalyst for NO_(X) reduction, the catalyst including a metal vanadate as an active site loaded on a support, and a method of synthesizing the same.

2. Description of the Related Art

Currently, a chemical process for efficiently, environment-friendly, and continuously converting nitrogen oxide (NO_(X)) and ammonia (NH₃) which are main causes of secondary fine dust, e.g., selective catalytic reduction of NO_(X) by NH₃ (NH₃-SCR) (see Reaction Formulas (1) and (2)), attracts much attention. 4NO+4NH₃+O₂→4N₂+6H₂O  (1) 2NO₂+4NH₃+O₂→3N₂+6H₂O  (2)

The NH₃-SCR process may be additionally improved by enhancing performance implementable by a currently used commercial catalyst. For example, the commercial catalyst used in the NH₃-SCR process of power plants, sintering furnaces, and vessels includes vanadium (V) oxide-WO₃/TiO₂ (where the V oxide includes at least one of V₂O₃, VO₂, and V₂O₅). As such, surface properties of the commercial catalyst are being improved. To this end, for example, V oxide used as an active site of the commercial catalyst may be structurally transformed. Specifically, a metal vanadate synthesized due to chemical binding of V oxide and metal oxide may be desirable as an active site of NH₃—SCR. More specifically, the metal vanadate is a composite oxide of V and another metal, and may solve, during NH₃-SCR, at least one of problems of the V oxide active site included in the commercial catalyst, e.g., 1) aggregation of the active site of the catalyst during NH₃-SCR due to a low melting point, 2) a low redox character, 3) a small amount of a Brφnsted acid site or a Lewis acid site, 4) slow NH₃-SCR at a low temperature (Reaction Formula (3)), 5) an insufficient resistance against poisoning of the catalyst surface by SO₂ included in an exhaust gas, 6) an insufficient resistance against poisoning of the catalyst surface by ammonium sulfate (AS; (NH₄)₂SO₄) or ammonium bisulfate (ABS; (NH₄)HSO₄) produced during NH₃-SCR based on chemical reactions expressed by Reaction Formulas (4) to (6), 7) an insufficient resistance against an alkaline compound included in the exhaust gas, 8) lack of structural stability of the V oxide active site or a support at a high temperature, and 9) an insufficient resistance against hydrothermal aging. For example, compared to the commercial catalyst, Cu₃V₂O₈ and Fe₂V₄O₁₃ may solve at least one of the problems 1) to 7), and ErVO₄ and TbVO₄ may solve at least one of the problems 8) and 9). NO+NO₂+2NH₃→2N₂+3H₂O  (3) SO₂+½O₂→SO₃  (4) SO₃+2NH₃+H₂O→(NH₄)₂SO₄  (5) SO₃+NH₃+H₂O→(NH₄)HSO₄  (6)

However, despite of various advantages of the metal vanadates as an active site of a catalyst, a method capable of decomposing AS and ABS poisoning the catalyst surface, at a low temperature has not been found.

SUMMARY

The present invention provides a heterogeneous catalyst for selective catalytic reduction of NO_(X) by NH₃ (NH₃-SCR), the catalyst having an excellent catalytic character compared to a commercial catalyst and using, as an active site, one of or a mixture of two or more of metal vanadates synthesizable at low costs, and a method of synthesizing the same. The present invention also provides a method of synthesizing a heterogeneous catalyst for NH₃-SCR, the catalyst 1) including at least one metal vanadate as an active site, and 2) being capable of decomposing ammonium sulfate (AS; (NH₄)₂SO₄) and ammonium bisulfate (ABS; (NH₄)HSO₄) produced during NH₃-SCR to poison the catalyst surface, at a low temperature. However, the scope of the present invention is not limited thereto.

According to an aspect of the present invention, there is provided a nitrogen oxide (NO_(X)) reduction catalyst including an active site including at least one of a metal vanadate expressed by [Chemical Formula 1] and a metal vanadate expressed by [Chemical Formula 2], and a support for loading the active site thereon. (M₁)_(X)V₂O_(X+5)  [Chemical Formula 1]

(where M₁ denotes one selected from among manganese (Mn), cobalt (Co), and nickel (Ni), and X denotes a real number having a value between 1 and 3.) (M₂)_(Y)VO₄  [Chemical Formula 2]

(where M₂ denotes one selected from among lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu), and Y denotes a real number having a value between 0.5 and 1.5.)

According to another aspect of the present invention, there is provided a nitrogen oxide (NO_(X)) reduction catalyst including a first active site including a metal vanadate expressed by [Chemical Formula 1], a second active site including a metal vanadate expressed by [Chemical Formula 2], and a support for loading both of the first and second active sites thereon. (M₁)_(X)V₂O_(X+5)  [Chemical Formula 1]

(where M₁ denotes one selected from among manganese (Mn), cobalt (Co), and nickel (Ni), and X denotes a real number having a value between 1 and 3.) (M₂)_(Y)VO₄  [Chemical Formula 2]

(where M₂ denotes one selected from among lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu), and Y denotes a real number having a value between 0.5 and 1.5.)

According to another aspect of the present invention, there is provided a nitrogen oxide (NO_(X)) reduction catalyst configured as a mixture of a first catalyst including a first active site including a metal vanadate expressed by [Chemical Formula 1], and a support for loading the first active site thereon, and a second catalyst including a second active site including a metal vanadate expressed by [Chemical Formula 2], and a support for loading the second active site thereon. (M₁)_(X)V₂O_(X+5)  [Chemical Formula 1]

(where M₁ denotes one selected from among manganese (Mn), cobalt (Co), and nickel (Ni), and X denotes a real number having a value between 1 and 3.) (M₂)_(Y)VO₄  [Chemical Formula 2]

(where M₂ denotes one selected from among lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu), and Y denotes a real number having a value between 0.5 and 1.5.)

The support may include oxide of a Group-15 or Group-16 element as a promoter, and the promoter may have a composition range of 1 wt % to 5 wt % based on the total weight of the support, or have a composition range of 0.5 wt % to 3 wt % based on a total weight of the NO_(X) reduction catalyst.

The Group-15 or Group-16 element may include at least one selected from the group consisting of or a combination of nitrogen (N), phosphorus (P), sulfur (S), arsenic (As), selenium (Se), antimony (Sb), tellurium (Te), bismuth (Bi), polonium (Po), moscovium (Mc), and livermorium (Lv).

At least a part of a surface of the NO_(X) reduction catalyst may be sulfated.

The support may include one of carbon (C), Al₂O₃, MgO, ZrO₂, CeO₂, TiO₂, and SiO₂.

The metal vanadate expressed by [Chemical Formula 1] or the metal vanadate expressed by [Chemical Formula 2] may be included by 10⁻⁴ parts by weight to 50 parts by weight based on 100 parts by weight of the support.

The support may have a porous structure.

According to another aspect of the present invention, there is provided a method of synthesizing a nitrogen oxide (NO_(X)) reduction catalyst.

The method includes preparing a mixture solution by mixing a vanadium (V) precursor solution and a metal precursor solution, adding the mixture solution with a material used for a support, and synthesizing a catalyst including a support having loaded thereon a metal vanadate expressed by [Chemical Formula 1] and serving as an active site, and/or a metal vanadate expressed by [Chemical Formula 2] and serving as an active site, by obtaining a solid from the mixture solution and calcining the solid.

The metal precursor solution may include a solution having dissolved therein one selected among manganese (Mn) salt, cobalt (Co) salt, and nickel (Ni) salt, or a solution having dissolved therein one selected among lanthanum (La) salt, cerium (Ce) salt, praseodymium (Pr) salt, neodymium (Nd) salt, promethium (Pm) salt, samarium (Sm) salt, europium (Eu) salt, gadolinium (Gd) salt, terbium (Tb) salt, dysprosium (Dy) salt, holmium (Ho) salt, erbium (Er) salt, thulium (Tm) salt, ytterbium (Yb) salt, and lutetium (Lu) salt.

According to another aspect of the present invention, there is provided a method of synthesizing a nitrogen oxide (NO_(X)) reduction catalyst, the method including preparing a mixture solution by mixing a vanadium (V) precursor solution, a first metal precursor solution, and a second metal precursor solution, adding the mixture solution with a material used for a support, and synthesizing a catalyst including a support having loaded thereon a metal vanadate expressed by [Chemical Formula 1] and serving as a first active site, and a metal vanadate expressed by [Chemical Formula 2] and serving as a second active site, by obtaining a solid from the mixture solution and calcining the solid.

The first metal precursor solution may include a solution having dissolved therein one selected among manganese (Mn) salt, cobalt (Co) salt, and nickel (Ni) salt, and the second metal precursor solution may include a solution having dissolved therein one selected among lanthanum (La) salt, cerium (Ce) salt, praseodymium (Pr) salt, neodymium (Nd) salt, promethium (Pm) salt, samarium (Sm) salt, europium (Eu) salt, gadolinium (Gd) salt, terbium (Tb) salt, dysprosium (Dy) salt, holmium (Ho) salt, erbium (Er) salt, thulium (Tm) salt, ytterbium (Yb) salt, and lutetium (Lu) salt.

The method may further include sulfating the solid after the solid is obtained and calcined.

The method may further include mixing the catalyst including the support having loaded thereon the metal vanadate expressed by [Chemical Formula 1], with the catalyst including the support having loaded thereon the metal vanadate expressed by [Chemical Formula 2].

The V precursor solution may include a solution having dissolved therein at least one of NH₄VO₃, NaVO₃, VCl₂, VCl₃, VBr₃, VCl₃.3C₄H₈O, VO(C₅H₇O₂)₂, VO(OC₂H₅)₃, VC₁₀H₁₀Cl₂, VC₁₈H₁₄I, VOCl₃, VOF₃, VO(OCH(CH₃)₂)₃, V(C₅H₇O₂)₃, VOSO₄, and V(C₅H₅)₂.

The Mn salt may include at least one of Mn(NO₃)₂, MnSO₄, MnI₂, Mn(C₁₁H₁₉O₂)₃, MnCl₂, C₁₀H₁₄MnO₄, Mn(C₅H₇O₂)₃, Mn(CH₃COO)₂, Mn(CH₃COO)₃, Mn(CH₃CO₂)₂, Mn[CH₃COCH═C(O)CH₃]₂, Mn(ClO₄)₂, MnF₃, Mn₂(CO)₁₀, MnC₃₂H₁₆N₈, MnC₂F₆O₆S₂, MnCO₃, MnBr₂, Li₂MnCl₄, MnF₂, MnC₃₂H₁₆ClN₈, Mn(HCO₂)₂Mn.XH₂O, Mn[C₆H₁₁(CH₂)₃CO₂]₂, MnC₁₆H₂₂, MnC₁₈H₂₆, Mn₂C₁₀O₁₀, MnC₃H₉O₁₂S₃, and KMnO₄.

The Co salt may include at least one of Co(NO₃)₂, CoBr₂, CoCl₂, Co(CH₃CO₂)₂, CO₂(CO)₈, Co(C₅H₇O₂)₃, CoSO₄, [Co(NH₃)₆]Cl₃, CoF₂, CoF₃, CoCO₃, CO₃(PO₄)₂, CO(ClO₄)₂, CO(BF₄)₂, CO(SCN)₂, CO(OH)₂, CO(NH₄)₂(SO₄)₂, CoC₅H₅(CO)₂, COC₂O₄, Co(CN)₂, CO(C₅H₇O₂)₂, CO(C₅HF₆O₂)₂, Co(C₅H₅)₂, CoC₂₀H₃₀Co, Co(H₂NCH₂CH₂NH₂)₃Cl₃, and [Co(NH₃)₆]Cl₃.

The Ni salt may include at least one of Ni(NO₃)₂, NiI₂, NiCl₂, Ni(OCOCH₃)₂, NiSO₄, NiO₂.XH₂O, Ni(C₅H₇O₂)₂, Ni(ClO₄)₂, NiBr₂, Ni(OH)₂, NiBr₂, Ni(NH₄)₂(SO₄)₂, NiCO₃.2Ni(OH)₂, 2NiCO₃.3Ni(OH)₂, NiF₂, and Ni[CH₃(CH₂)₆CO₂]₂.

The La salt may include at least one of LaF₃, LaB₆, LaCl₃, La(CH₃CO₂)₃, LaI₃, La₂(C₂O₄)₃, La(CF₃SO₃)₃, La(NO₃)₃, La(C₉H₂₁O₃), La(C₅H₇O₂)₃, LaBr₃, LaPO₄, La₂(CO₃)₃, La(OH)₃, and La₂(SO₄)₃.

The Ce salt may include at least one of CeF₃, Ce(NH₄)₂(NO₃)₆, CeF₄, CeCl₃, Ce(CH₃CO₂)₃, CeI₃, Ce(SO₄)₂, Ce₂(C₂O₄)₃, Ce(NO₃)₃, Ce(C₅H₇O₂)₃, CeBr₃, Ce₂(CO₃)₃, Ce(OH)₄, Ce(NH₄)₄(SO₄)₄, and Ce₂(SO₄)₃.

The Pr salt may include at least one of PrCl₃, Pr(NO₃)₃, PrCl₃, Pr(C₅H₇O₂)₃, and Pr₂(SO₄)₃.

The Nd salt may include at least one of NdF₃, NdCl₃, Nd(NO₃)₃, Nd(CH₃CO₂)₃, NdCl₃, Nd(NO₃)₃, and Nd₂(SO₄)₃.

The Sm salt may include at least one of Sm₁₂, Sm₁₃, SmCl₃, Sm(NO₃)₃, Sm(CH₃CO₂)₃, SmPO₄, Sm(C₉H₂₁O₃), Sm₂(SO₄)₃, and Sm(C₅H₇O₂)₃.

The Eu salt may include at least one of EuI₂, EuF₃, EuBr₂, EuBr₃, EuCl₂, EuCl₃, Eu(NO₃)₃, Eu(CH₃CO₂)₃, Eu(C₅H₇O₂)₃, and Eu₂(SO₄)₃.

The Gd salt may include at least one of GdCl₃, GdF₃, GdCl₃, Gd(NO₃)₃, Gd(CH₃CO₂)₃, Gd(C₅H₇O₂)₃, Gd₂(SO₄)₃, Gd(C₅H₇O₂)₃, and Gd(OH)₃.

The Tb salt may include at least one of TbCl₃, TbF₃, Tb(NO₃)₃, Tb(CH₃CO₂)₃, Tb(C₅H₇O₂)₃, and Tb₂(SO₄)₃.

The Dy salt may include at least one of DyF₃, DyCl₂, Dy(NO₃)₃, DyCl₃, and Dy(CH₃CO₂)₃.

The Ho salt may include at least one of HoCl₃, HoBr₃, HoF₃, Ho(NO₃)₃, Ho(ClO₄)₃, and Ho(CH₃CO₂)₃.

The Er salt may include at least one of ErF₃, ErCl₃, ErBr₃, and Er(NO₃)₃.

The thulium salt may include at least one of TmI₂, TmBr₃, TmF₃, TmCl₃, Tm(NO₃)₃, Tm(CH₃CO₂)₃, Tm₂(CO₃)₃, and Tm₂(SO₄)₃.

The Yb salt may include at least one of YbCl₃, YbF₃, YbI₂, Yb(NO₃)₃, Yb(CH₃CO₂)₃, and Yb(C₉H₂₁O₃).

The Lu salt may include at least one of LuCl₃, Lu(CH₃CO₂)₃, LuF₃, LuCl₃, Lu(NO₃)₃, and Lu(C₅H₇O₂)₃.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present invention will become more apparent by describing in detail embodiments thereof with reference to the attached drawings in which:

FIGS. 1A to 1C are high-resolution transmission electron microscopy (HRTEM) images of catalysts synthesized according to Embodiments 1 to 3 of the present invention;

FIGS. 2A and 2B are scanning electron microscopy (SEM) images of images of catalysts synthesized according to Embodiments 13 and 15 of the present invention;

FIGS. 3A and 3B are HRTEM images of catalysts synthesized according to Embodiments 18 and 23 of the present invention;

FIG. 4 is a graph showing X-ray diffraction (XRD) patterns of the catalysts synthesized according to Embodiments 1 to 3 of the present invention;

FIG. 5 is a graph showing XRD patterns of the catalysts synthesized according to Embodiments 13 and 15 of the present invention;

FIGS. 6A to 6C images showing selected area electron diffraction (SAED) patterns of the catalysts synthesized according to Embodiments 1 to 3 of the present invention;

FIG. 7 includes a graph and image showing a XRD pattern and a SAED pattern of the catalyst synthesized according to Embodiment 23 of the present invention; and

FIGS. 8 to 18 are graphs showing selective catalytic reduction of NO_(X) by NH₃ (NH₃-SCR) performance analysis results of catalysts according to embodiments of the present invention and comparative examples.

DETAILED DESCRIPTION

The following detailed descriptions of the invention will be made with reference to the accompanying drawings illustrating specific embodiments of the invention by way of example. These embodiments will be described in detail such that the invention can be carried out by one of ordinary skill in the art. It should be understood that various embodiments of the invention are different, but are not necessarily mutually exclusive.

For example, a specific shape, structure, and characteristic of an embodiment described herein may be implemented in another embodiment without departing from the scope of the invention. In addition, it should be understood that a position or placement of each component in each disclosed embodiment may be changed without departing from the scope of the invention. Accordingly, there is no intent to limit the invention to the following detailed descriptions. The scope of the invention is defined by the appended claims and encompasses all equivalents that fall within the scope of the appended claims. In the drawings, like reference numerals denote like functions, and the sizes of elements may be exaggerated for convenience of explanation.

Hereinafter, to allow one of ordinary skill in the art to easily carry out the invention, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

A nitrogen oxide (NO_(X)) reduction catalyst according to an embodiment of the present invention includes an active site corresponding to a region onto which a reactant is adsorbed and from which a product is detached after reaction, and a support for loading the active site thereon.

A NO_(X) reduction catalyst according to a first embodiment of the present invention includes a metal vanadate (or a composite oxide of vanadium (V)) including one metal selected from among manganese (Mn), cobalt (Co), and nickel (Ni), and V, and expressed by [Chemical Formula 1], as an active site. Such a metal vanadate is called a “metal vanadate A”. (M₁)_(X)V₂O_(X+5)  [Chemical Formula 1]

(where M₁ denotes one selected from among Mn, Co, and Ni, and X denotes a real number having a value between 1 and 3.)

For example, the metal vanadate A includes at least one selected from among MnV₂O₆, Mn₂V₂O₇, Mn₃V₂O₈, CoV₂O₆, Co₂V₂O₇, Co₃V₂O₈, NiV₂O₆, Ni₂V₂O₇, and Ni₃V₂O₈.

The metal vanadate A used as the active site may be synthesized in various ways by adjusting stoichiometry of M₁ (e.g., Mn, Co, or Ni) and V.

A NO_(X) reduction catalyst according to a second embodiment of the present invention includes a metal vanadate (or a composite oxide of V) including one metal selected from among lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu), and V, and expressed by [Chemical Formula 2], as an active site. Such a metal vanadate is called a “metal vanadate B”. (M₂)_(Y)VO₄  [Chemical Formula 2]

(where M₂ denotes one selected from among La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and Y denotes a real number having a value between 0.5 and 1.5.)

For example, the metal vanadate B may include at least one selected from among LaVO₄, CeVO₄, PrVO₄, NdVO₄, PmVO₄, SmVO₄, EuVO₄, GdVO₄, TbVO₄, DyVO₄, HoVO₄, ErVO₄, TmVO₄, YbVO₄, and LuVO₄.

The metal vanadate B used as the active site may be synthesized based on 1:1 stoichiometry of M₂ (e.g., La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, or Yb) and V. However, to increase a metal or V site which is coordinatively unsaturated and thus is capable of desirably interacting with NO_(X), NH₃, ammonium sulfate (AS; (NH₄)₂SO₄), or ammonium bisulfate (ABS; (NH₄)HSO₄), the metal vanadate B may be synthesized in such a manner that the stoichiometry of M₂:V has a range between 0.5:1 and 1.5:1.

According to an embodiment of the present invention, the active site substantially includes only a metal vanadate. For example, at least 90 wt % of the material of the active site may be the metal vanadate. Specifically, the metal vanadate may be included by at least 95 wt %, and more desirably, by at least 99 wt %, and the remnant may include a material unavoidable in a synthesis process.

Since the active site includes a composite oxide of V and one of metals, an excellent catalytic character is achieved compared to a case in which V oxide and another metal oxide (e.g., Mn oxide, Co oxide, Ni oxide, Yb oxide, or Ce oxide) are present as different materials.

A NO_(X) reduction catalyst according to a third embodiment of the present invention includes a mixture of a first catalyst including a first active site including at least one metal vanadate A, and a support for loading the first active site thereon, and a second catalyst including a second active site including at least one metal vanadate B, and a support for loading the second active site thereon.

The first catalyst including the metal vanadate A as an active site may achieve an excellent catalytic character at a low temperature equal to or lower than 300° C. On the contrary, the second catalyst including the metal vanadate B as an active site may achieve an excellent catalytic character at a temperature equal to or higher than 300° C.

Therefore, when a mixture of the first catalyst and the second catalyst at an appropriate ratio is used as a catalyst, the catalyst may efficiently operate in a wide temperature range from a low temperature to a high temperature.

A mixing ratio of the mixed catalyst according to the third embodiment may be variously changed depending on an environment (e.g., a temperature or an atmosphere) or a purpose of application of the catalyst. For example, a weight ratio of the second catalyst to the first catalyst may vary within a range from 0.1:99.9 to 99.1:0.1.

A NO_(X) reduction catalyst according to a fourth embodiment of the present invention has a structure in which a first active site including at least one metal vanadate A and a second active site including at least one metal vanadate B are both loaded on one support.

Differently from the third embodiment in which the first and second catalysts respectively including the first and second active sites loaded on different supports are mixed, according to the fourth embodiment, heterogeneous metal vanadates belonging to different groups are loaded on one support as active sites.

Similarly to the catalyst according to the third embodiment, the NO_(X) reduction catalyst according to the fourth embodiment may efficiently operate in a wide temperature range from a low temperature to a high temperature because the first active site having an excellent high-temperature character and the second active site having an excellent low-temperature character are both loaded on one support.

The first and second active sites may be randomly distributed in the support, and a relative weight ratio of the second active site to the first active site may vary within a range from 0.1:99.9 to 99.1:0.1.

The above-described metal vanadate according to an embodiment of the present invention may be prepared using various methods. For example, the metal vanadate may be synthesized using one or more of hydrothermal synthesis, solvothermal synthesis, a mechano-chemical method (e.g., ball-milling), non-templated or templated synthesis, a wet or dry impregnation method, and a thermal decomposition method using a Mn—V, Co—V, or Ni—V based complex).

The metal vanadate may be dispersed in a porous support to be described below, and may have a diameter (maximum diameter) of 0.1 nm to 500 μm. In this case, the metal vanadate may have a composition range of 10⁻⁴ parts by weight to 50 parts by weight based on 100 parts by weight of the support.

The above-described NO_(X) reduction catalyst according to an embodiment of the present invention may further include a promoter. The active site of the NO_(X) reduction catalyst needs to have a low activity in adsorption and oxidation reaction of sulfur dioxide (SO₂) included in a flue gas. Ammonia (NH₃) serving as a reducing agent may react with sulfur trioxide (SO₃) based on Chemical Reaction Formulas (3) to (5) to produce AS (or ABS) on the catalyst surface, and AS may be irreversibly adsorbed onto the active site of the catalyst at a low temperature equal to or lower than 300° C. Adsorbed AS may reduce the activity of the catalyst by hindering adsorption of NO_(X) and the reducing agent, e.g., NH₃. SO₃ produced due to oxidation of SO₂ may be bond to water vapor included in the flue gas, to produce sulfuric acid (H₂SO₄) and corrode a rear-end system of a selective catalytic reduction (SCR) process. SO₂+½O₂→SO₃  (3) SO₃+2NH₃+H₂O→(NH₄)₂SO₄  (4) SO₃+NH₃+H₂O→(NH₄)HSO₄  (5)

The promoter may serve to increase a resistance against poisoning by SO₂ or the AS during catalytic reaction. For example, the promoter may reduce binding energy between SO₂ and the surface of the catalyst. As such, oxidation reaction of SO₂ (Reaction Formula (3)), which may occur during low-temperature SCR, may be minimized. Furthermore, the promoter may minimize the amount of AS (Reaction Formula (4)) or ABS (Reaction Formula (5)) adsorbed onto the catalyst surface due to reaction between SO₂ and NH₃ and thus prevent a reduction in activity of the catalyst due to poisoning of the catalyst surface. In addition, the promoter may be added as an element of the catalyst surface, which is capable of decomposing AS or ABS at a low temperature.

The promoter includes oxide of a Group-15 or Group-16 element. The Group-15 or Group-16 element may include at least one selected from the group consisting of or a combination of nitrogen (N), phosphorus (P), sulfur (S), arsenic (As), selenium (Se), antimony (Sb), tellurium (Te), bismuth (Bi), polonium (Po), moscovium (Mc), and livermorium (Lv).

The promoter may be included by 10⁻⁴ parts by weight to 50 parts by weight based on 100 parts by weight of the support. Specifically, the promoter may be included by 3 parts by weight or less, and more desirably, by 0.5 parts by weight to 2 parts by weight.

The support serves to disperse and load the metal vanadate and the promoter thereon. The active site of the catalyst needs to have a high redox character for appropriate adsorption and conversion of NO_(X). In this case, when the catalyst is synthesized by dispersing the metal vanadate in an appropriate support, reactive oxygen (O₂) species in the support may be appropriately supplied to the active site. That is, the redox character of the catalyst may be improved. At the same time, when the catalyst is synthesized by highly dispersing the metal vanadate in the support, catalyst efficiency may be further improved. Therefore, a NO_(X) reduction catalyst including a support having a character capable of providing the above environment may be synthesized.

The support may include carbon (C) or metal oxide. The metal oxide may be one selected from among Al₂O₃, MgO, ZrO₂, CeO₂, TiO₂, and SiO₂.

The NO_(X) reduction catalyst according to an embodiment of the present invention may have a morphological character of a large surface area. The larger the surface area, the faster adsorption of a reactant (e.g., NO_(X) or NH₃) and the higher a reaction rate. As such, NO_(X) reduction efficiency may be improved. To ensure a large surface area, the catalyst may have a porous structure. For example, a porous structure having a large surface area may be implemented by configuring the support as aggregates obtained by calcining a powder material.

The NO_(X) reduction catalyst according to an embodiment of the present invention may be functionalized by sulfating the surface thereof. The sulfation process according to the present invention refers to functionalization of the catalyst with SO_(Y) ²⁻. In this specification, “functionalization” may refer to a process for improving performance of a catalyst by increasing the number of active sites of the catalyst or improving, for example, a reactant-catalyst adsorption character. For example, when the NO_(X) reduction catalyst of the present invention is sulfated and is functionalized with SO_(Y) ²⁻, the catalyst surface may become advantageous for adsorption and conversion of NO_(X), and new active sites may be created.

An S—O binding character in SO_(Y) ²⁻ species bound to metal species on the catalyst surface may be adjusted based on functionalization with SO_(Y) ²⁻ by sulfating the surface. Specifically, the SO_(Y) ²⁻ species on the catalyst surface are bound to the metal species of the catalyst in the form of bi-dentate binding when they have an ionic character, and are bound to the metal species of the catalyst in the form of mono-dentate binding when they have a covalent character. Selective catalytic reduction of NO_(X) by NH₃ (NH₃-SCR) performance of the catalyst may depend on distribution of the binding types on the catalyst.

In this case, according to an embodiment of the present invention, the sulfation process may be performed using a reaction gas including SO₂ and 02. The reaction gas may have a concentration of SO₂ and 02 ranging from 10 ppm to 10⁵ ppm, a flow rate ranging from 10⁻⁵ mL min⁻¹ to 10⁵ mL min⁻¹, and a pressure ranging from 10⁻⁵ bar to 10⁵ bar. The sulfation process may be performed in a temperature range from 200° C. to 800° C. for 0.1 hour to 24 hours.

When conditions for the sulfation process of the catalyst do not reach the above-described ranges, the SO_(Y) ²⁻ functionalization effect of the catalyst may be insufficient. Otherwise, when the conditions exceed the above-described ranges, oxygen species (O_(α)) for improving a redox character of the catalyst surface during NH₃-SCR or improving NO₂ production efficiency for fast NH₃-SCR of Reaction Formula (7) may be eliminated due to excessive functionalization of the support surface. Therefore, the sulfation process of the catalyst may be performed within the above-described condition ranges. NO+NO₂+2NH₃→2N₂+3H₂O  (7)

The catalyst modified due to the sulfation and SO_(Y) ²⁻ functionalization process additionally produce SO_(Y) ²⁻—NH₄ species. The SO_(Y) ²⁻—NH₄ species serve as a Bronsted acid site capable of adsorbing the reducing agent, e.g., NH₃. That is, the sulfated and functionalized catalyst according to the present invention may increase the number of reaction active sites compared to a non-functionalized catalyst. Furthermore, the catalyst modified due to functionalization with SO_(Y) ²⁻ may additionally produce metal-SO_(Y) ²⁻ species and thus improve an oxidation/reduction character compared to a non-functionalized catalyst. In addition, the metal-SO_(Y) ²⁻ species may improve NO₂ production efficiency for fast NH₃-SCR of Reaction Formula (7).

That is, the number of acid sites may be adjusted or a binding strength between reactants (e.g., NO_(X) and NH₃) and poisoning materials (e.g., AS and ABS) may be adjusted based on SO_(Y) ²⁻ (Y-3 or 4) functionalization conditions. Therefore, when an optimal metal vanadate for NH₃-SCR is synthesized, during NH₃-SCR, 1) a plurality of Brφnsted acid sites may be provided, 2) a plurality of coordinatively unsaturated Lewis acid sites may be provided, 3) an optimal reaction strength with reactants desirable for efficient execution of a NO_(X) turnover cycle may be provided, 4) NO oxidation efficiency desirable for fast SCR may be implemented, and 5) an element of the catalyst surface, which is capable of decomposing the poisoning materials (e.g., AS and ABS) of the catalyst surface at a low temperature, may be provided.

Even when poisoned by AS or ABS produced during catalytic reaction, the NO_(X) reduction catalyst according to an embodiment of the present invention may decompose AS or ABS at a low temperature lower than 300° C. and thus may achieve an excellent regeneration effect for recovering a catalytic character to that before being poisoned, compared to general catalysts. That is, after being poisoned by AS or ABS produced during reduction of NO_(X), even when a regeneration process is performed in an oxygen and nitrogen atmosphere, the general catalysts may not easily recover catalytic characters to those before being poisoned. However, in the NO_(X) reduction catalyst according to an embodiment of the present invention, even after being poisoned by AS or ABS, when a regeneration process is performed in an oxygen and nitrogen atmosphere at a temperature lower than 300° C., AS or ABS is decomposed and the catalytic character is recovered. This means that the NO_(X) reduction catalyst of the present invention may be reused without replacement by merely performing a regeneration process after the catalyst operates for a certain time, and thus a life span of the catalyst may be remarkably increased.

A method of synthesizing a NO_(X) reduction catalyst, according to an embodiment of the present invention, will now be described.

A method of synthesizing a NO_(X) reduction catalyst, according to a first embodiment of the present invention, may include the following operations.

Initially, a V precursor solution and a metal precursor solution A including a metal selected from among Mn, Co, and Ni are prepared.

The V precursor solution may be, for example, a solution obtained by dissolving a V compound in a solvent. The V compound includes, for example, NH₄VO₃, NaVO₃, VCl₂, VCl₃, VBr₃, VCl₃.3C₄H₈O, VO(C₅H₇O₂)₂, VO(OC₂H₅)₃, VC₁₀H₁₀Cl₂, VC₁₈H₁₄I, VOCl₃, VOF₃, VO(OCH(CH₃)₂)₃, V(C₅H₇O₂)₃, VOSO₄, or V(C₅H₅)₂.

The metal precursor solution A is used to provide one of Mn, Co, and Ni used for the catalyst, and may be a solution obtained by dissolving one of Mn salt, Co salt, and Ni salt in a solvent.

The Mn salt may include, for example, Mn(NO₃)₂, MnSO₄, MnI₂, Mn(C₁₁H₁₉O₂)₃, MnCl₂, C₁₀H₁₄MnO₄, Mn(C₅H₇O₂)₃, Mn(CH₃COO)₂, Mn(CH₃COO)₃, Mn(CH₃CO₂)₂, Mn[CH₃COCH═C(O)CH₃]₂, Mn(ClO₄)₂, MnF₃, Mn₂(CO)₁₀, MnC₃₂H₁₆N₈, MnC₂F₆O₆S₂, MnCO₃, MnBr₂, Li₂MnCl₄, MnF₂, MnC₃₂H₁₆ClN₈, Mn(HCO₂)₂Mn.XH₂O, Mn[C₆H₁₁(CH₂)₃CO₂]₂, MnC₁₆H₂₂, MnC₁₈H₂₆, Mn₂C₁₀O₁₀, MnC₃H₉O₁₂S₃, or KMnO₄.

The Co salt may include, for example, Co(NO₃)₂, CoBr₂, CoCl₂, Co(CH₃CO₂)₂, Co₂(CO)₈, Co(C₆H₇O₂)₃, CoSO₄, [Co(NH₃)₆]Cl₃, COF₂, COF₃, CoCO₃, CO₃(PO₄)₂, CO(ClO₄)₂, CO(BF₄)₂, CO(SCN)₂, CO(OH)₂, CO(NH₄)₂(SO₄)₂, CoC₅H₅(CO)₂, CoC₂O₄, Co(CN)₂, CO(C₅H₇O₂)₂, CO(C₅HF₆O₂)₂, Co(C₅H₅)₂, CoC₂₀H₃₀Co, Co(H₂NCH₂CH₂NH₂)₃Cl₃, or [Co(NH₃)₆]Cl₃.

The Ni salt may include, for example, Ni(NO₃)₂, NiI₂, NiCl₂, Ni(OCOCH₃)₂, NiSO₄, NiO₂.XH₂O, Ni(C₆H₇O₂)₂, Ni(ClO₄)₂, NiBr₂, Ni(OH)₂, NiBr₂, Ni(NH₄)₂(SO₄)₂, NiCO₃.2Ni(OH)₂, 2NiCO₃.3Ni(OH)₂, NiF₂, or Ni[CH₃(CH₂)₆CO₂]₂.

Then, a mixture solution A is prepared by mixing the prepared V precursor solution and metal precursor solution A. The mixture solution A is added with a material used for a support, is sufficiently stirred, and then is dehydrated to obtain a solid including a single metal vanadate. A NO_(X) reduction catalyst having the single metal vanadate dispersed therein may be synthesized by calcining the obtained solid.

A method of synthesizing a NO_(X) reduction catalyst, according to a second embodiment of the present invention, may equal that of the first embodiment except that a different metal precursor solution is used. In the second embodiment, a metal precursor solution B to be mixed with the V precursor solution includes a metal selected from among La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

The metal precursor solution B is used to provide one of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu used for the catalyst, and may be a solution obtained by dissolving one of La salt, Ce salt, Pr salt, Nd salt, Pm salt, Sm salt, Eu salt, Gd salt, Tb salt, Dy salt, Ho salt, Er salt, thulium salt, Yb salt, and Lu salt in a solvent.

The La salt may include, for example, LaF₃, LaB₆, LaCl₃, La(CH₃CO₂)₃, LaI₃, La₂(C₂O₄)₃, La(CF₃SO₃)₃, La(NO₃)₃, La(C₉H₂₁O₃), La(C₅H₇O₂)₃, LaBr₃, LaPO₄, La₂(CO₃)₃, La(OH)₃, or La₂(SO₄)₃.

The Ce salt may include, for example, CeF₃, Ce(NH₄)₂(NO₃)₆, CeF₄, CeCl₃, Ce(CH₃CO₂)₃, CeI₃, Ce(SO₄)₂, Ce₂(C₂O₄)₃, Ce(NO₃)₃, Ce(C₆H₇O₂)₃, CeBr₃, Ce₂(CO₃)₃, Ce(OH)₄, Ce(NH₄)₄(SO₄)₄, or Ce₂(SO₄)₃.

The Pr salt may include, for example, PrCl₃, Pr(NO₃)₃, PrCl₃, Pr(C₅H₇O₂)₃, or Pr₂(SO₄)₃.

The Nd salt may include, for example, NdF₃, NdCl₃, Nd(NO₃)₃, Nd(CH₃CO₂)₃, NdCl₃, Nd(NO₃)₃, or Nd₂(SO₄)₃.

The Sm salt may include, for example, Sm₁₂, Sm₁₃, SmCl₃, Sm(NO₃)₃, Sm(CH₃CO₂)₃, SmPO₄, Sm(C₉H₂₁O₃), Sm₂(SO₄)₃, or Sm(C₅H₇O₂)₃.

The Eu salt may include, for example, EuI₂, EuF₃, EuBr₂, EuBr₃, EuCl₂, EuCl₃, Eu(NO₃)₃, Eu(CH₃CO₂)₃, Eu(C₅H₇O₂)₃, or Eu₂(SO₄)₃.

The Gd salt may include, for example, GdCl₃, GdF₃, GdCl₃, Gd(NO₃)₃, Gd(CH₃CO₂)₃, Gd(C₅H₇O₂)₃, Gd₂(SO₄)₃, Gd(C₅H₇O₂)₃, or Gd(OH)₃.

The Tb salt may include, for example, TbCl₃, TbF₃, Tb(NO₃)₃, Tb(CH₃CO₂)₃, Tb(C₅H₇O₂)₃, or Tb₂(SO₄)₃.

The Dy salt may include, for example, DyF₃, DyCl₂, Dy(NO₃)₃, DyCl₃, or Dy(CH₃CO₂)₃.

The Ho salt may include, for example, HoCl₃, HoBr₃, HoF₃, Ho(NO₃)₃, Ho(ClO₄)₃, or Ho(CH₃CO₂)₃.

The Er salt may include, for example, ErF₃, ErCl₃, ErBr₃, or Er(NO₃)₃.

The Tm salt may include, for example, TmI₂, TmBr₃, TmF₃, TmCl₃, Tm(NO₃)₃, Tm(CH₃CO₂)₃, Tm₂(CO₃)₃, or Tm₂(SO₄)₃.

The Yb salt may include, for example, YbCl₃, YbF₃, YbI₂, Yb(NO₃)₃, Yb(CH₃CO₂)₃, or Yb(C₉H₂₁O₃).

The Lu salt may include, for example, LuCl₃, Lu(CH₃CO₂)₃, LuF₃, LuCl₃, Lu(NO₃)₃, or Lu(C₅H₇O₂)₃.

A method of synthesizing a NO_(X) reduction catalyst, according to a third embodiment of the present invention, may include the following operations.

A mixture solution A is prepared by mixing a V precursor solution and a metal precursor solution A, and a mixture solution B is prepared by mixing the V precursor solution and a metal precursor solution B. The mixture solutions A and B are added with a material used for a support, are sufficiently stirred, and then are dehydrated to obtain a solid A and a solid B each including a single metal vanadate. A NO_(X) reduction catalyst having the single metal vanadates dispersed therein may be synthesized by mechanically mixing and then calcining, or calcining and then mechanically mixing the obtained solids A and B.

A method of synthesizing a NO_(X) reduction catalyst, according to a fourth embodiment of the present invention, may include the following operations.

A mixture solution is prepared by mixing a V precursor solution, a metal precursor solution A, and a metal precursor solution B. The mixture solution is added with a material used for a support, is sufficiently stirred, and then is dehydrated to obtain a solid. A NO_(X) reduction catalyst having a mixture of single metal vanadates dispersed therein may be synthesized by calcining the obtained solid.

As another method, a mixture solution A is prepared by mixing a V precursor solution and a metal precursor solution A, and a mixture solution B is prepared by mixing the V precursor solution and a metal precursor solution B. The mixture solution A (or the mixture solution B) is added with a material used for a support, is sufficiently stirred, is added with the mixture solution B (or the mixture solution A), is sufficiently stirred, and then is dehydrated to obtain a solid. A NO_(X) reduction catalyst having a mixture of single metal vanadates dispersed therein may be synthesized by calcining the obtained solid.

In the above-described methods, a promoter may be created in a catalyst by including a Group-15 or Group-16 element in a support to be added to a mixture solution. For example, the support including the promoter may be prepared by mixing powder of a material used for the support, with a solution in which a compound of the Group-15 or Group-16 element is dissolved, and then performing stirring, dehydration, and calcination processes.

After the catalyst is synthesized, a SO_(Y) ²⁻ functionalization process may be further performed to improve a catalytic character. The SO_(Y) ²⁻ functionalization process may be performed by exposing the surface of the catalyst to a process gas including SO₂ and O₂ under certain flow rate and pressure conditions. Table 1 shows condition ranges for SO_(Y) ²⁻ functionalization.

TABLE 1 Flow rate of Exposure Process SO₂ content O₂ content Pressure process gas time temperature (ppm) (Vol %) (bar) (mL min⁻¹) (h) (° C.) 10 to 10⁵ 10⁻⁵ to 90 10⁻⁵ to 10⁵ 10⁻⁵ to 10⁵ 0.1 to 24 200 to 800

When conditions for SO_(Y) ²⁻ functionalization do not reach a temperature of 200° C., a time of 0.1 hour, 10 ppm of SO₂, 10⁻⁵ Vol % of O₂, a flow rate of 10⁻⁵ mL min⁻¹, or a pressure of 10⁻⁵ bar, the SO_(Y) ²⁻ functionalization effect of the catalyst surface may be insufficient. Otherwise, when the conditions exceed a temperature of 800° C., a time of 24 hours, 10⁵ ppm of SO₂, 90 Vol % of O₂, a flow rate of 10⁵ mL min⁻¹, or a pressure of 10⁵ bar, oxygen species (O_(α)) for increasing SCR activity may be eliminated due to excessive SO_(Y) ²⁻ functionalization of the surface of the support. Therefore, the SO_(Y) ²⁻ functionalization process of the catalyst surface may be performed within the above-described condition ranges.

In addition, to improve a character of the catalyst surface while the catalyst is being synthesized, the amount of a metal/V precursor added to a synthetic solution may be adjusted. Specifically, metal and V may be added to the synthetic solution to stoichiometrically have a range between 0.5:1 and 1.5:1.

Hereinafter, the present invention will be described in detail by explaining embodiments of the invention. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein.

Embodiments 1 to 3: Synthesis of Mn, Co, and Ni Catalysts

Mixture solutions are prepared by mixing 170 mL of distilled water in which 2.3 mmol of NH₄VO₃ is dissolved, with 70 mL of distilled water in which 1.15 mmol of Mn salt (e.g., Mn(NO₃)₂.6H₂O), Co salt (e.g., Co(NO₃)₂.6H₂O), and Ni salt (e.g., Ni(NO₃)₂.6H₂O) are dissolved, and then are stirred for 1 hour. After being completely stirred, the mixture solutions are added with 6 g of anatase TiO₂ powder, are stirred for 24 hours, and then are dehydrated. Catalysts of Embodiments 1, 2, and 3 are synthesized by calcining solids obtained after dehydration, at 500° C. for 5 hours. The catalysts of Embodiments 1, 2, and 3 are characterized in that TiO₂ supports having an anatase phase are used and MnV₂O₆, CoV₂O₆, and NiV₂O₆ are included in the supports as active sites. In the following description, for convenience of explanation, the catalysts of Embodiments 1, 2, and 3 are called a Mn catalyst, a Co catalyst, and a Ni catalyst, respectively.

Comparative Example 1: Synthesis of W Catalyst

A catalyst having a V content similar to that of the catalysts of Embodiments 1 to 3 and including tungsten (W) as an active site is synthesized as a comparative example. Specifically, 0.46 g of NH₄VO₃, 0.67 g of (NH₄)₁₀(H₂W₁₂O₄₂).4H₂O, and 0.84 g of C₂H₂O₄.2H₂O are dissolved in 100 mL of distilled water, 9.3 g of anatase TiO₂ powder is added, and then stirring and dehydration processes are performed. Thereafter, a catalyst including W is synthesized by performing a calcination process at 500° C. for 5 hours. In the catalyst of Comparative Example 1, V oxide and W oxide serving as an active site are provided as a mechanical mixture of different materials. In the following description, for convenience of explanation, the catalyst of Comparative Example 1 is called a W catalyst.

Embodiments 4 to 6: Synthesis of Mn(S), Co(S), and Ni(S) Catalysts

The Mn, Co, and Ni catalysts synthesized according to Embodiments 1 to 3 are mounted in reactors, are exposed to SO₂ and O₂ diluted in nitrogen (N₂) and simultaneously supplied at a flow rate of 500 mLmin⁻¹, at atmospheric pressure at 500° C. for 45 minutes, and then are cooled to room temperature in a N₂ atmosphere. In the exposure process, the content of SO₂ is 500 ppm and the content of 02 is 3 vol %. For convenience of explanation, the catalysts of Embodiments 4 to 6, which are SO_(Y) ²-functionalized based on the above conditions, are called a Mn(S) catalyst, a Co(S) catalyst, and a Ni(S) catalyst, respectively.

Comparative Example 2: Synthesis of W(S)-A Catalyst

A catalyst of Comparative Example 2, which is synthesized by functionalizing the surface of the W catalyst of Comparative Example 1 with SO_(Y) ²⁻ in the same manner as Embodiments 4 to 6, is called a W(S)-A catalyst.

Embodiments 7 to 9: Synthesis of Mn—Se, Mn—Se(S, 30), and Mn—Se(S,500) Catalysts

To prepare TiO₂ including Se as a promoter, a TiO₂ support including 3 wt % of Se based on the total weight of TiO₂ is prepared by adding 48.5 g of TiO₂ to 500 mL of distilled water in which 4.19 g of SeCl₄ is dissolved (to include 1.5 g of Se), performing stirring and dehydration processes, and then performing a calcination process at 300° C. for 3 hours. A Mn catalyst including Se (called a Mn—Se catalyst, Embodiment 7) is synthesized by using 6 g of the support in the same manner as Embodiment 1 except that a calcination process is performed at 400° C. for 3 hours. The Mn—Se catalyst is mounted in a reactor, is exposed to SO₂ and O₂ diluted in N₂ and simultaneously supplied at a flow rate of 500 mLmin⁻¹, at atmospheric pressure at 400° C. for 45 minutes, and then is cooled to room temperature in a N₂ atmosphere. In the exposure process, the content of SO₂ is 30 ppm or 500 ppm and the content of 02 is 3 vol %. Catalysts synthesized by functionalizing the surface of the Mn—Se catalyst with SO_(Y) ²⁻ by using 30 ppm and 500 ppm of SO₂ are called a Mn—Se(S,30) catalyst (Embodiment 8) and a Mn—Se(S,500) catalyst (Embodiment 9), respectively.

Embodiments 10 and 11: Synthesis of Mn—Se(S,500)-300 and Mn—Se(S,500)-500 Catalysts

The Mn—Se catalyst of Embodiment 7 is mounted in a reactor, is exposed to SO₂ and 02 diluted in N₂ and simultaneously supplied at a flow rate of 500 mLmin⁻¹, at atmospheric pressure at 300° C. or 500° C. for 45 minutes, and then is cooled to room temperature in a N₂ atmosphere. In the exposure process, the content of SO₂ is 500 ppm and the content of 02 is 3 vol %. Catalysts synthesized by functionalizing the surface of the Mn—Se catalyst with SO_(Y) ²⁻ at temperatures of 300° C. and 500° C. are called a Mn—Se(S,500)-300 (Embodiment 10) and a Mn—Se(S,500)-500 (Embodiment 11), respectively.

Embodiment 12: Synthesis of Mn—Se(S,500)-Na Catalyst

A Mn—Se(S,500)-Na catalyst is synthesized by intentionally poisoning the surface of the Mn—Se(S,500) catalyst of Embodiment 9 by supplying 60 mol % of sodium (Na) species based on a total molar mass of Mn, V, and Se included in the catalyst, to the catalyst surface. Specifically, the Mn—Se(S,500)-Na catalyst of Embodiment 12 is synthesized by calcining a solid obtained by mechanically mixing 1.5 g of the Mn—Se(S) catalyst with 0.07413 g of NaNO₃, at 400° C. for 3 hours.

Comparative Examples 3 and 4: Synthesis of W(S,30)-B and W(S,500)-B Catalysts

A catalyst synthesized by functionalizing the surface of the W catalyst of Comparative Example 1 with SO_(Y) ²⁻ in the same manner as Embodiment 8 or 9 is called as a W(S,XXX)-B catalyst. Specifically, a catalyst synthesized by functionalizing the surface of the W catalyst with SO_(Y) ²⁻ by using 30 ppm of SO₂ is called a W(S,30)-B catalyst (Comparative Example 3), and a catalyst synthesized by functionalizing the surface of the W catalyst with SO_(Y) ²⁻ by using 500 ppm of SO₂ is called a W(S,500)-B catalyst (Comparative Example 4).

Comparative Example 5: Synthesis of W(S,500)-B—Na Catalyst

A W(S,500)-B—Na catalyst of Comparative Example 5 is synthesized by poisoning the surface of the W(S,500)-B catalyst of Comparative Example 4 with Na in the same manner as Embodiment 12.

Embodiment 13: Synthesis of Yb Catalyst

A mixture solution is prepared by adding 50 mL of distilled water in which 1.96 mmol of NH₄VO₃ is dissolved, to 50 mL of distilled water in which 1.96 mmol of Yb(NO₃)₃.5H₂O is dissolved, and then is stirred for 2 hours by fixing a pH value at 8. After being completely stirred, the mixture solution is added with 4.56 g of anatase TiO₂ powder, is stirred for 18 hours, and then is dehydrated. A Yb catalyst of Embodiment 13, which includes TiO₂ as a support and includes YbVO₄ as an active site, is synthesized by calcining a solid obtained after dehydration, at 500° C. for 5 hours.

Embodiment 14: Synthesis of Mn/Yb Catalyst

A solid obtained by mechanically mixing 1.5 g of the Mn catalyst of Embodiment 1 including 2 wt % of V (active site: MnV₂O₆), with 1.5 g of the Yb catalyst of Embodiment 13 (active site: YbVO₄) is called a Mn/Yb catalyst of Embodiment 14.

Embodiment 15: Synthesis of Yb—Se(S,500) Catalyst

A solid (Yb—Se) synthesized by using 4.56 g of a TiO₂ support including 3 wt % of Se (promoter) based on the total weight of TiO₂, in the same manner as Embodiment 13 except that a calcination process is performed at 400° C. for 3 hours is mounted in a reactor, is exposed to SO₂ and 02 diluted in N₂ and simultaneously supplied at a flow rate of 500 mLmin⁻¹, at atmospheric pressure at 400° C. for 45 minutes, and then is cooled to room temperature in a N₂ atmosphere. In the exposure process, the content of SO₂ is 500 ppm and the content of 02 is 3 vol %. The finally obtained catalyst is called a Yb—Se(S,500) catalyst of Embodiment 15.

Embodiment 16: Synthesis of Mn—Se/Yb—Se(S,500) Catalyst

A solid obtained by mechanically mixing 1.5 g of the Mn—Se catalyst of Embodiment 7 including 2 wt % of V (active site: MnV₂O₆; promoter: Se), with 1.5 g of the solid Yb—Se used to synthesize the catalyst of Embodiment 15 (active site: YbVO₄; promoter: Se) is mounted in a reactor, is exposed to SO₂ and 02 diluted in N₂ and simultaneously supplied at a flow rate of 500 mLmin⁻¹, at atmospheric pressure at 400° C. for 45 minutes, and then is cooled to room temperature in a N₂ atmosphere. In the exposure process, the content of SO₂ is 500 ppm and the content of 02 is 3 vol %. The finally obtained catalyst is called a Mn—Se/Yb—Se(S,500) catalyst of Embodiment 16.

Embodiments 17 to 22: Synthesis of Mn—Sb₁, Mn—Sb₃, Mn—Sb₅, Mn—Sb₁(S,500), Mn—Sb₃(S,500), and Mn—Sb₅(S,500) Catalysts

To prepare TiO₂ supports including 1 wt %, 3 wt %, and 5 wt % of Sb based on the total weight of TiO₂, 49.5 g of TiO₂ is added to 500 mL of acetic acid in which 1.23 g of Sb(CH₃COO)₃ is dissolved (to include 0.5 g of Sb), 48.5 g of TiO₂ is added to 500 mL of acetic acid in which 3.68 g of Sb(CH₃COO)₃ is dissolved (to include 1.5 g of Sb), or 47.5 g of TiO₂ is added to 500 mL of acetic acid in which 6.14 g of Sb(CH₃COO)₃ is dissolved (to include 2.5 g of Sb), and then stirring and dehydration processes are performed and a calcination process is performed at 500° C. for 5 hours. The prepared supports are called Sb₁, Sb₃, and Sb₅ supports. Catalysts of Embodiments 17 to 19 are synthesized by using 6 g of the supports in the same manner as Embodiment 1. The synthesized catalysts are called Mn—Sb₁, Mn—Sb₃, and Mn—Sb₅ catalysts. The catalysts of Embodiments 17 to 19 are characterized in that TiO₂ supports having an anatase phase and including 1 wt %, 3 wt %, and 5 wt % of Sb are used and MnV₂O₆ is included in the supports as an active site. Catalysts of Embodiments 20 to 22, which are synthesized by functionalizing the surfaces of the Mn—Sb₁, Mn—Sb₃, and Mn—Sb₅ catalysts with SO_(Y) ²⁻ in the same manners as Embodiments 4 to 6, are called Mn—Sb₁(S,500), Mn—Sb₃(S,500), and Mn—Sb₅(S,500) catalysts, respectively.

Embodiments 23 and 24: Synthesis of CeVO₄ and CeVO₄(S,500) Catalysts

A TiO₂ support including 2 wt % of Sb based on the total weight of TiO₂ is prepared by adding 9.8 g of TiO₂ to 150 mL of acetic acid in which 0.49 g of Sb(CH₃COO)₃ is dissolved (to include 0.2 g of Sb), performing stirring and dehydration processes, and then performing a calcination process at 500° C. for 5 hours. A mixture solution is prepared by adding 9.46 g of the support to 100 mL of distilled water in which 3.93 mmol of NH₄VO₃ is dissolved and 200 mL of distilled water in which 1.96 mmol of Ce salt (e.g., Ce(NO₃)₃.6H₂O) is dissolved, and then is stirred for 2 hours and is dehydrated. A CeVO₄ catalyst of Embodiment 23 is synthesized by calcining a solid obtained after dehydration, at 500° C. for 5 hours. The catalyst of Embodiment 23 is characterized in that a TiO₂ support having an anatase phase and including Sb is used and CeVO₄ is included in the support as an active site. A catalyst of Embodiment 24, which is synthesized by functionalizing the surface of the CeVO₄ catalyst with SO_(Y) ²⁻ in the same manner as Embodiments 4 to 6, is called a CeVO₄(S,500) catalyst.

Embodiments 25 and 26: Synthesis of Mn—Sb₃/CeVO₄ and Mn—Sb₃/CeVO₄(S,500) Catalysts

A mixture solution is prepared by adding 50 mL of distilled water in which 5.86 g of the Sb₃ support of Embodiment 17 is dispersed, to 70 mL of distilled water in which 0.59 mmol of Ce salt (e.g., Ce(NO₃)₃.6H₂O) is dissolved and 170 mL of distilled water in which 1.18 mmol of V salt (e.g., NH₄VO₃) is dissolved. The mixture solution is stirred for 18 hours, is added with 120 mL of distilled water in which 0.59 mmol of Mn salt (e.g., Mn(NO₃)₂.6H₂O) and 1.18 mmol of V salt (e.g., NH₄VO₃) is dissolved, is stirred for 18 hours, and then is dehydrated. A Mn—Sb₃/CeVO₄ catalyst of Embodiment 25 is synthesized by calcining a solid obtained after dehydration, at 500° C. for 5 hours. The catalyst of Embodiment 25 is characterized in that a TiO₂ support having an anatase phase and including 3 wt % of Sb is used and MnV₂O₆ and CeVO₄ are included in the support as active sites. A catalyst of Embodiment 26, which is synthesized by functionalizing the surface of the Mn—Sb₃/CeVO₄ catalyst with SO_(Y) ²⁻ in the same manner as Embodiments 4 to 6, is called a Mn—Sb₃/CeVO₄(S,500) catalyst.

Experimental Example 1: Analysis of Catalytic Characters

Morphologies of the catalysts synthesized according to Embodiments 1 to 3 are analyzed using high-resolution transmission electron microscopy (HRTEM), and results thereof are shown in FIGS. 1A to 1C, respectively. Morphologies of the catalysts synthesized according to Embodiments 13 and 15 are analyzed using scanning electron microscopy (SEM), and results thereof are shown in FIGS. 2A and 2B, respectively. Morphologies of the catalysts synthesized according to Embodiments 18 and 23 are analyzed using HRTEM, and results thereof are shown in FIGS. 3A and 3B, respectively.

Referring to FIGS. 1 to 3, it is shown that TiO₂ agglomerates having grain sizes (maximum diameters) of several hundred nanometers to several hundred micrometers configure porous supports in the synthesized catalysts.

To check porosity of the catalysts of Embodiments 1 to 3, 13, 18, and 23, Brunauer-Emmett-Teller (BET) surface areas and Brunauer-Joyner-Halenda (BJH) pore volumes are measured by performing N₂ physisorption tests. In addition, components of the catalysts synthesized according to Embodiments 1 to 3, 13, 18, and 23 are analyzed using X-ray fluorescence (XRF). Results thereof are shown in Table 2.

TABLE 2 BET surface area BJH pore volume Catalyst component content (wt %) Embodiment 1 63 m² g⁻¹ 0.3 cm³ g⁻¹ V: 1.9 (±0.1), Mn: 0.9 (±0.1) Embodiment 2 64 m² g⁻¹ 0.3 cm³ g⁻¹ V: 1.9 (±0.1), Co: 1.3 (±0.4) Embodiment 3 66 m² g⁻¹ 0.3 cm³ g⁻¹ V: 1.9 (±0.1), Ni: 1.5 (±0.5) Embodiment 13 63 m² g⁻¹ 0.3 cm³ g⁻¹ V: 1.9 (±0.1), Yb: 6.7 (±0.3) Embodiment 18 58 m² g⁻¹ 0.2 cm³ g⁻¹ V: 2.1 (±0.1), Mn: 0.9 (±0.2) Embodiment 23 61 m² g⁻¹ 0.3 cm³ g⁻¹ V: 2.1 (±0.1), Ce: 3.4 (±0.2)

The results of measuring the BET surface areas and the BJH pore volumes show that the catalysts synthesized according to Embodiments 1 to 3, 13, 18, and 23 have porous structures. The results of analyzing the components show that the catalysts have almost the same content, e.g., 2 wt %, of V based on total weights of the catalysts.

It is shown that V:metal (Mn, Co, and Ni) molar ratios of the Mn, Co, Ni, and Mn—Sb₃ catalysts have values close to a theoretical molar ratio (V:metal=2:1). It is also shown that a V:Yb molar ratio of the Yb catalyst also has a value close to a theoretical molar ratio (V:Yb=1:1). As such, it is shown that MnV₂O₆, CoV₂O₆, NiV₂O₆, and YbVO₄ are successfully dispersed in the porous TiO₂ supports on the surfaces of the catalysts of Embodiments 1 to 3, 13, and 18.

Meanwhile, the CeVO₄ catalyst provides a V:Ce molar ratio of 2:1 due to lack of Ce compared to a theoretical V:Ce molar ratio (V:Ce=1:1) of CeVO₄. This means that additional Lewis acid sites may be created on Ce or V sites of CeVO₄ dispersed in the surface of the TiO₂ support, by adjusting stoichiometry of Ce/V.

Crystal structures of Embodiments 1 to 3 are analyzed using an X-ray diffractomer, and X-ray diffraction (XRD) patterns obtained as results thereof are shown in FIG. 4. Crystal structures of Embodiments 13 and 15 are analyzed using an X-ray diffractomer, and XRD patterns obtained as results thereof are shown in FIG. 5. A crystal structure of Embodiment 23 is analyzed using an X-ray diffractomer, and an XRD pattern obtained as a result thereof is shown in FIG. 7.

Referring to FIGS. 4, 5, and 7, tetragonal crystal planes corresponding to an anatase phase, which mean a TiO₂ support, are observed from all of Embodiments 1 to 3, 13, 15, and 23. Meanwhile, crystal planes meaning MnV₂O₆, CoV₂O₆, NiV₂O₆, and CeVO₄ crystal grains are not observed from Embodiments 1 to 3, and 23. This may be because the size or content of metal vanadate crystal grains dispersed in the support is too small for XRD analysis. Therefore, the Mn, Co, and Ni catalysts of Embodiments 1 to 3 and the CeVO₄ catalyst of Embodiment 23 are analyzed using selected area electron diffraction (SAED) patterns, and results thereof are shown in FIGS. 6A to 6C, and 7, respectively.

Referring to FIG. 6, monoclinic (2 0 −1), (0 0 1), and (1 1 1) crystal planes of MnV₂O₆ are observed from the Mn catalyst, monoclinic (0 0 1) and (2 0 0) crystal planes of CoV₂O₆ are observed from the Co catalyst, triclinic (−1 0 1), (0 1 1), and (1 1 1) crystal planes of NiV₂O₆ are observed from the Ni catalyst, and tetragonal (1 0 1) and (2 0 0) crystal planes of CeVO₄ are observed from the CeVO₄ catalyst.

In addition, tetragonal crystal planes corresponding to an anatase phase of TiO₂, which mean a TiO₂ support, are observed from all of Embodiments 1 to 3. Specifically, Embodiment 1 shows (1 0 1) and (0 0 4) crystal planes, Embodiments 2 and 3 show (1 0 1), (1 0 3), and (0 0 4) crystal planes, and Embodiment 23 shows (1 0 1) and (1 0 3) crystal planes. These results are consistent with the XRD pattern results of FIGS. 4 and 7.

As shown in FIGS. 4 and 7, a pattern of another material other than a metal vanadate, e.g., V oxide or oxide of another metal (Mn, Co, Ni, or Ce), is not observed from Embodiments 1 to 3, and 23. That is, Embodiments 1 to 3, and 23 of the present invention show that Vanadium oxides and oxides of metal (Mn, Co, Ni, or Ce) other than Vanadium form a composite oxide and are not merely provided as a mixture of different materials.

Differently from the XRD patterns of Embodiments 1 to 3, and 23, tetragonal YbVO₄ crystal planes are observed from the XRD patterns of Embodiments 13 and 15 (see FIG. 5). In addition, a pattern of another material other than YbVO₄, e.g., V oxide or Yb oxide, is not observed from Embodiments 13 and 15. That is, Embodiments 13 and 15 of the present invention show that V oxide and Yb oxide are transformed into a composite oxide, e.g., YbVO₄, and are not provided as a mixture of different materials.

NH₃-SCR performance analysis results of the catalysts according to Embodiments 1 to 26 of the present invention and Comparative Examples 1 to 5 will now be described with reference to FIGS. 8 to 18.

Experimental Example 2: NH₃-SCR Performance Analysis (1)

Performance of a NH₃-SCR process is measured using the catalysts of Embodiments 1 to 3. In a temperature range of 150° C. to 400° C., NO_(X) conversions X_(NOX) and N₂ selectivities S_(N2) in a case when H₂O is injected are shown in FIG. 8. The NH₃-SCR process is performed under conditions that a reaction fluid includes 800 ppm of NO_(x), 800 ppm of NH₃, 3 vol % of O₂, 6 vol % of H₂O, and an inert gas of N₂, a total flow rate is 500 mLmin⁻¹, and a space velocity is 60,000 hr⁻¹.

Referring to FIG. 8, although a considerable amount of water vapor (H₂O) is included in the reaction gas, all of Embodiments 1 to 3 show desirable activities at a temperature equal to or lower than 400° C. Specifically, it is shown that the NO_(X) conversions X_(NOX) are equal to or higher than 50% at a temperature equal to or higher than 250° C. and reach 90% at a temperature equal to or higher than 350° C. It is also shown that the N₂ selectivities S_(N2) are almost 100% in the entire temperature range. This means that the catalysts of Embodiments 1 to 3 are usable as NH₃-SCR catalysts applied to power plants, sintering furnaces, and vessels.

Experimental Example 3: NH₃-SCR Performance Analysis (2)

Performance of a NH₃-SCR process is measured using the catalysts of Embodiments 4 to 6 under the same conditions as Experimental Example 2, and NO_(X) conversions X_(NOX) and N₂ selectivities S_(N2) are shown in FIG. 9. The surfaces of all of the catalysts of Embodiments 4 to 6 are poisoned by SO₂ or are SO_(Y) ²⁻-functionalized by SO₂/O₂ before NH₃-SCR. (Specific conditions thereof are described above in Embodiments 4 to 6.) Referring to FIG. 9, similarly to Experimental Example 2, although a considerable amount of water vapor (H₂O) is included during reaction, desirable activities are shown at a temperature equal to or lower than 400° C. Specifically, it is shown that the NO_(X) conversions X_(NOX) are equal to or higher than 50% at a temperature equal to or higher than 250° C. and reach 90% at a temperature equal to or higher than 350° C. It is also shown that the N₂ selectivities S_(N2) are almost 100% in the entire temperature range. This means that the surfaces of the catalysts of Embodiments 4 to 6 are preferably functionalized with SO_(Y) ²⁻ and poisoning thereof by SO₂ is minimized. This also means that the catalysts of Embodiments 4 to 6 are applicable to power plants, sintering furnaces, and vessels and are usable as NH₃-SCR catalysts for reducing NO_(X) in an exhaust gas including a considerable amount of SO₂.

Experimental Example 4: NH₃-SCR Performance Analysis (3)

Performance of a NH₃-SCR process is measured using the catalysts of Embodiments 4 to 6 and the catalyst of Comparative Example 2. The NH₃-SCR process is performed under conditions that a reaction fluid includes 800 ppm of NO_(x), 800 ppm of NH₃, 500 ppm of SO₂, 3 vol % of O₂, 6 vol % of H₂O, and an inert gas of N₂, a total flow rate is 500 mLmin⁻¹, and a space velocity is 60,000 hr⁻¹. NO_(X) conversions X_(NOX) and N₂ selectivities S_(N2) are shown in FIG. 10.

Referring to FIG. 10, all of the catalysts of Embodiments 4 to 6 show excellent catalytic characters as catalysts for reducing NO_(X) in an exhaust gas including considerable amounts of water vapor (H₂O) and SO₂. It is shown that the N₂ selectivities S_(N2) of the catalysts of Embodiments 4 to 6 are almost 100% in the entire reaction temperature range. It is also shown that the NO_(X) conversions X_(NOX) of the catalysts of Embodiments 4 to 6 are similar to or only slightly different (by 15% or less) from that of the commercial catalyst of Comparative Example 2 in a temperature range of 250° C. to 400° C. This means that poisoning of the surfaces of the catalysts of Embodiments 4 to 6 by SO₂ is minimized due to functionalization with SO_(Y) ²⁻. As such, it is shown that the catalysts of Embodiments 4 to 6 of the present invention may replace the high-priced commercial catalyst of Comparative Example 2.

Experimental Example 5: NH₃-SCR Performance Analysis (4)

Performance of a NH₃-SCR process is measured using the catalysts of Embodiments 9 to 11 and the catalyst of Comparative Example 4. The surfaces of all of the catalysts of Embodiments 9 to 11 and Comparative Example 4 are poisoned by SO₂ or are SO_(Y) ²⁻-functionalized by SO₂/O₂ before NH₃-SCR, and a functionalization temperature used in this case is changed to 300° C. (Embodiment 10), to 400° C. (Embodiment 9 and Comparative Example 4), and to 500° C. (Embodiment 11).

The NH₃-SCR process is performed under conditions that a reaction fluid includes 800 ppm of NO_(x), 800 ppm of NH₃, 3 vol % of O₂, 6 vol % of H₂O, and an inert gas of N₂, a total flow rate is 500 mLmin⁻¹, and a space velocity is 60,000 hr⁻¹. NO_(X) conversions X_(NOX) and N₂ selectivities S_(N2) are shown in FIG. 11.

Referring to FIG. 11, the catalysts of Embodiments 9 to 11 are catalysts to which Se is added as a promoter, and show increased activities in a low reaction temperature range compared to the Mn(S) catalyst of Embodiment 4 to which Se in not added. This means that a larger amount of an acid site is created on the surfaces of the catalysts of Embodiments 9 to 11 or an improved redox character is achieved due to addition of Se.

In addition, the catalysts of Embodiments 9 to 11 may adjust NH₃-SCR activities by changing a temperature used for SO₄ ²⁻ functionalization. Meaningfully, the NO_(X) conversions X_(NOX) of the catalysts of Embodiments 9 and 10 are similar to or only slightly different (by 10% or less) from that of the commercial catalyst of Comparative Example 4 in a temperature range of 220° C. to 400° C. As such, it is shown that the catalysts of Embodiments 9 and 10 of the present invention may replace the high-priced commercial catalyst of Comparative Example 4.

Experimental Example 6: NH₃-SCR Performance Analysis (5)

Performance of a NH₃-SCR process is measured using the Mn—Se catalysts of Embodiments 7 to 9 and the W catalysts of Comparative Examples 1, 3, and 4. The NH₃-SCR process is performed under conditions that a reaction fluid includes 800 ppm of NO_(x), 800 ppm of NH₃, 3 vol % of O₂, 6 vol % of H₂O, and an inert gas of N₂, a total flow rate is 500 mLmin⁻¹, and a space velocity is 60,000 hr⁻¹. In this case, the content of SO₂ in the reaction fluid is changed to 0 ppm, to 30 ppm, and to 500 ppm.

NO_(X) conversions X_(NOX) and N₂ selectivities S_(N2) in a temperature range of 150° C. to 400° C. are shown in FIG. 11.

Referring to FIG. 12, the Mn—Se catalysts of Embodiments 7 to 9 show similar or gradually increasing NH₃-SCR performance values at a temperature equal to or higher than 180° C. as the concentration of SO₂ is increased from 0 ppm to 30 ppm and to 500 ppm. This means that, as a Mn—Se catalyst is functionalized with SO_(Y) ²⁻, 1) a larger amount of an acid site is created on the catalyst surface, 2) a NO_(X) turnover cycle is improved based on desirable binding force with a reactant, 3) an improved redox character is achieved, or 4) a resistance against SO₂, AS, or ABS is increased.

On the contrary, the W catalyst of Comparative Example 1, which is not sulfated, and the W catalyst of Comparative Example 3, which is sulfated using 30 ppm of SO₂, show similar NH₃-SCR performance values at a temperature equal to or higher than 180° C. However, compared to the W catalysts of Comparative Examples 1 and 3, the W catalyst of Comparative Example 4, which is sulfated using 500 ppm of SO₂, shows remarkably lowered NH₃-SCR performance values at a temperature equal to or lower than 200° C. This means that, compared to the commercial catalysts, the Mn—Se catalysts proposed by the present invention may provide desirable properties after SO_(Y) ²⁻ functionalization and thus may replace the high-priced commercial catalysts.

Experimental Example 7: NH₃-SCR Performance Analysis (6)

Performance of a NH₃-SCR process is measured using the Mn—Se(S,500)-Na catalyst of Embodiment 12 and the W(S,500)-B—Na catalyst of Comparative Example 5. In this case, the NH₃-SCR process is performed under conditions that a reaction fluid includes 800 ppm of NO_(x), 800 ppm of NH₃, 500 ppm of SO₂, 3 vol % of O₂, 6 vol % of H₂O, and an inert gas of N₂, a total flow rate is 500 mLmin⁻¹, and a space velocity is 60,000 hr⁻¹. NO_(X) conversions X_(NOX) and N₂ selectivities S_(N2) of the catalysts of Embodiments 9 and 12 and Comparative Examples 4 and 5 in a temperature range of 150° C. to 400° C. are shown in FIG. 13.

Referring to FIG. 13, compared to the Mn—Se(S,500) catalyst of Embodiment 9 and the W(S,500)-B catalyst of Comparative Example 4, the Mn—Se(S,500)-Na catalyst of Embodiment 12 and the W(S,500)-B—Na catalyst of Comparative Example 5, the surfaces of which are poisoned by Na, show lowered NH₃-SCR performance values, and this may be because of Na poisoning. However, relatively, the catalyst of Embodiment 12 shows excellent performance values compared to the catalyst of Comparative Example 5. This means that, in the Mn—Se(S,500) catalyst proposed by the present invention, after SO_(Y) ²⁻ functionalization, 1) binding between the catalyst surface and Na is minimized by minimizing distribution of acid sites having strong binding force with an alkaline compound, and 2) a desirable resistance against Na poisoning is achieved compared to the commercial catalyst of Comparative Example 4. As such, it is shown that the catalyst according to an embodiment of the present invention may have an excellent catalytic character to replace the high-priced commercial catalyst.

Experimental Example 8: NH₃-SCR Performance Analysis (7)

Performance of a NH₃-SCR process is measured using the Mn catalyst of Embodiment 1, the Yb catalyst of Embodiment 13, and the Mn/Yb catalyst of Embodiment 14. In a temperature range of 150° C. to 400° C., NO_(X) conversions X_(NOX) and N₂ selectivities S_(N2) in a case when H₂O is injected are shown in FIG. 14. The NH₃-SCR process is performed under conditions that a reaction fluid includes 800 ppm of NO_(x), 800 ppm of NH₃, 3 vol % of O₂, 6 vol % of H₂O, and an inert gas of N₂, a total flow rate is 500 mLmin⁻¹, and a space velocity is 60,000 hr⁻¹.

Referring to FIG. 14, although a considerable amount of water vapor (H₂O) is included, it is shown that the N₂ selectivities S_(N2) of all catalysts are almost 100% in the entire temperature range. In addition, differently from Embodiment 1 in which MnV₂O₆ showing a desirable activity at a temperature equal to or lower than 400° C. serves as an active site, Embodiment 13 in which YbVO₄ serves as an active site shows a low activity compared to Embodiment 1.

Specifically, it is shown that the NO_(X) conversions X_(NOX) of Embodiments 1 and 13 differ by 30% to 60% in a temperature range of 200° C. to 400° C. This means that YbVO₄ showing an excellent NH₃-SCR activity in a high temperature range may not be easily used as an active site of a catalyst due to a low NO_(X) conversion X_(NOX) in a low temperature range.

However, it is shown that the NO_(X) conversion X_(NOX) of Embodiment 14 in which MnV₂O₆ and YbVO₄ active sites are mixed is increased from that of Embodiment 13 by 10% to 40% in a temperature range of 200° C. to 400° C. This means that a mixture of MnV₂O₆ and YbVO₄ active sites at a desirable ratio may effectively increase the NH₃-SCR activity in low and high temperature ranges and may be broadly used as a NH₃-SCR catalyst for heavy equipment and vehicles as well as power plants, sintering furnaces, and vessels.

Experimental Example 9: NH₃-SCR Performance Analysis (8)

Performance of a NH₃-SCR process is measured using the Mn—Se(S,500) catalyst of Embodiment 9, the Yb—Se(S,500) catalyst of Embodiment 15, and the Mn—Se/Yb—Se(S,500) catalyst of Embodiment 16, commonly including Se as a promoter and respectively including MnV₂O₆, YbVO₄, and a mixture of MnV₂O₆ and YbVO₄ as active sites. (Specific conditions for synthesizing the Mn—Se/Yb—Se(S,500) catalyst are described above in Embodiment 16.) The surfaces of all of the catalysts of Embodiments 9, 15, and 16 are poisoned by SO₂ or are SO_(Y) ²⁻-functionalized by SO₂/O₂ before NH₃-SCR.

In this case, the NH₃-SCR process is performed under conditions that a reaction fluid includes 800 ppm of NO_(x), 800 ppm of NH₃, 500 ppm of SO₂, 3 vol % of O₂, 6 vol % of H₂O, and an inert gas of N₂, a total flow rate is 500 mLmin⁻¹, and a space velocity is 60,000 hr⁻¹. NO_(X) conversions X_(NOX) and N₂ selectivities S_(N2) of the catalysts of Embodiments 9, 15, and 16 in a temperature range of 150° C. to 400° C. are shown in FIG. 15.

Referring to FIG. 15, although considerable amounts of SO₂ and water vapor (H₂O) are included, it is shown that the N₂ selectivities S_(N2) of all catalysts are equal to or higher than 95% in the entire temperature range. In addition, differently from Embodiment 9 in which MnV₂O₆ showing a desirable activity at a temperature equal to or lower than 400° C. serves as an active site, Embodiment 15 in which YbVO₄ serves as an active site shows a low activity compared to Embodiment 9.

Specifically, it is shown that the NO_(X) conversions X_(NOX) of Embodiments 9 and 15 differ by 35% to 70% in a temperature range of 200° C. to 400° C. This means that YbVO₄ showing an excellent NH₃-SCR activity in a high temperature range may not be easily used as an active site of a catalyst due to a low NO_(X) conversion X_(NOX) in a low temperature range. However, it is shown that the NO_(X) conversion X_(NOX) of Embodiment 16 in which MnV₂O₆ and YbVO₄ active sites are mixed is increased from that of Embodiment 15 by 10% to 55% in a temperature range of 200° C. to 400° C. This means that a mixture of MnV₂O₆ and YbVO₄ active sites at a desirable ratio may effectively increase the NH₃-SCR activity in an environment including SO₂ in low and high temperature ranges and may be broadly used as a NH₃-SCR catalyst for heavy equipment and vehicles as well as power plants, sintering furnaces, and vessels.

Experimental Example 10: NH₃-SCR Performance Analysis (9)

Performance of a NH₃-SCR process is measured using the Mn—Sb₁ catalyst of Embodiment 17, the Mn—Sb₃ catalyst of Embodiment 18, and the Mn—Sb₅ catalyst of Embodiment 19, commonly including MnV₂O₆ as an active site and respectively including 1 wt %, 3 wt %, and 5 wt % of Sb based on the total weight of TiO₂ (about 0.5 wt %, 1.5 wt %, and 3 wt % of Sb based on a total weight of the catalyst), as promoters, and results thereof are compared to that of the Mn catalyst of Embodiment 1.

The surfaces of all of the catalysts of Embodiments 1, and 17 to 19 are poisoned by SO₂ or are SO_(Y) ²⁻-functionalized by SO₂/O₂ at 500° C. before NH₃-SCR.

In this case, the NH₃-SCR process is performed under conditions that a reaction fluid includes 800 ppm of NO_(x), 800 ppm of NH₃, 500 ppm of SO₂, 3 vol % of O₂, 6 vol % of H₂O, and an inert gas of N₂, a total flow rate is 500 mLmin⁻¹, and a space velocity is 60,000 hr⁻¹.

NO_(X) conversions X_(NOX) and N₂ selectivities S_(N2) of the catalysts of Embodiments 4, and 20 to 22 in a temperature range of 180° C. to 400° C. are shown in FIG. 16.

Referring to FIG. 16, the catalysts of Embodiments 20 to 22 show excellent catalytic characters as catalysts for reducing NO_(X) in an exhaust gas including considerable amounts of water vapor (H₂O) and SO₂. It is shown that the N₂ selectivities S_(N2) of the catalysts of Embodiments 20 to 22 are almost 100% in the entire reaction temperature range. It is also shown that the NO_(X) conversions X_(NOX) of the catalysts of Embodiments 20 to 22 are higher than that of the catalyst of Embodiment 4 not including a Sb promoter, by 10% to 30% in a temperature range of 180° C. to 250° C.

This means that, after functionalization with SO_(Y) ²⁻, compared to the catalyst of Embodiment 4 not including a Sb promoter, in the catalysts of Embodiments 20 to 22 including Sb promoters, 1) a larger amount of an acid site is present on the catalyst surface, 2) an improved redox character is achieved, 3) poisoning by SO₂ is minimized, or 4) a resistance against SO₂, AS, or ABS is increased.

As such, it is shown that the promoter included in the catalyst may achieve an excellent effect when the content thereof is in a range of 1 wt % to 5 wt %, and more desirably, in a range of 1 wt % to 3 wt %.

Experimental Example 11: NH₃-SCR Performance Analysis (10)

Performance of a NH₃-SCR process is measured using the Mn—Sb₃ catalyst of Embodiment 18, the CeVO₄ catalyst of Embodiment 23, and the Mn—Sb₃/CeVO₄ catalyst of Embodiment 25, commonly including Sb as a promoter and respectively including MnV₂O₆, CeVO₄, and MnV₂O₆ and CeVO₄ as active sites, and results thereof are compared to that of the W(S)-A catalyst of Comparative Example 2.

The catalyst of Embodiment 25 is obtained not based on mechanical mixing but based on chemical synthesis, and has a structure in which active sites, e.g., MnV₂O₆ and CeVO₄, are randomly distributed in a support, e.g., TiO₂.

All of the catalysts of Embodiments 18, 23, and 25 and Comparative Example 2 have almost the same V content, e.g., about 2 wt %, and the surfaces thereof are poisoned by SO₂ or are SO_(Y) ²⁻-functionalized by SO₂/O₂ at 500° C. before NH₃-SCR. In this case, the NH₃-SCR process is performed under conditions that a reaction fluid includes 800 ppm of NO_(x), 800 ppm of NH₃, 500 ppm of SO₂, 3 vol % of O₂, 6 vol % of H₂O, and an inert gas of N₂, a total flow rate is 500 mLmin⁻¹, and a space velocity is 60,000 hr⁻¹.

NO_(X) conversions X_(NOX) and N₂ selectivities S_(N2) of the catalysts of Embodiments 21, 24, and 26 and Comparative Example 2 in a temperature range of 180° C. to 400° C. are shown in FIG. 17.

Referring to FIG. 17, the catalysts of Embodiments 21, 24, and 26 show excellent catalytic characters as catalysts for reducing NO_(X) in an exhaust gas including considerable amounts of water vapor (H₂O) and SO₂. It is shown that the N₂ selectivities S_(N2) of the catalysts of Embodiments 21, 24, and 26 are almost 100% in the entire reaction temperature range. It is also shown that the NO_(X) conversions X_(NOX) of the catalysts of Embodiments 21, 24, and 26 are almost 100% (at a temperature equal to or higher than 300° C.) similarly to that of the commercial catalyst of Comparative Example 2, or are higher than that of the commercial catalyst of Comparative Example 2 by 10% to 30% (at a temperature lower than 300° C.) in a temperature range of 180° C. to 400° C.

This means that, due to functionalization of the surfaces of the catalysts of Embodiments 21, 24, and 26 with SO_(Y) ²⁻, 1) a larger amount of an acid site is created on the catalyst surface, 2) a NO_(X) turnover cycle is improved based on desirable binding force with a reactant, 3) an improved redox character is achieved, 4) poisoning by SO₂ is minimized, or 5) a resistance against SO₂, AS, or ABS is increased.

This also means that the catalysts of Embodiments 21, 24, and 26 of the present invention may replace the high-priced commercial catalyst of Comparative Example 2. In addition, this means that metal vanadate active sites proposed by the present invention (e.g., MnV₂O₆ and CeVO₄) may coexist on the support surface based on chemical synthesis, and a NH₃-SCR activity at a low temperature may be controlled by changing a relative ratio of the metal vanadates (e.g., a relative amount ratio of MnV₂O₆ and CeVO₄).

Experimental Example 12: NH₃-SCR Performance Analysis (11)

Performance of a NH₃-SCR process is measured at 220° C. by using the Mn—Sb₃ catalyst of Embodiment 18 and the CeVO₄ catalyst of Embodiment 23, commonly including Sb as a promoter and respectively including MnV₂O₆ and CeVO₄ as active sites, and results thereof are compared to that of the W catalyst of Comparative Example 1 at 220° C.

In this case, the NH₃-SCR process is performed under conditions that a reaction fluid includes 800 ppm of NO_(x), 800 ppm of NH₃, 3 vol % of O₂, 6 vol % of H₂O, and an inert gas of N₂, a total flow rate is 500 mLmin⁻¹, and a space velocity is 60,000 hr⁻¹. Thereafter, to poison the surfaces of the catalysts of Embodiments 18 and 23 and Comparative Example 1 with SO₂/AS/ABS at 180° C. during NH₃-SCR, the reaction fluid is added with 500 ppm of SO₂ and is supplied to the catalyst surface for 3 hours, and the NH₃-SCR performance of the poisoned catalysts is measured at 220° C. in the reaction fluid (not including SO₂).

Then, to regenerate the catalysts poisoned with SO₂/AS/ABS, at a low temperature (e.g., 260° C.), a fluid satisfying the following conditions is supplied. A fluid including only 3 vol % of O₂ and an inert gas of N₂ and controlled to a total flow rate of 500 mLmin⁻¹ and a space velocity of 60,000 hr⁻¹ is supplied to the surface of the Mn—Sb₃ catalyst of Embodiment 18 for 1 hour. A fluid including only 3 vol % of O₂ and an inert gas of N₂ and controlled to a total flow rate of 500 mLmin⁻¹ and a space velocity of 60,000 hr⁻¹ is supplied to the surfaces of the CeVO₄ catalyst of Embodiment 23 and the W catalyst of Comparative Example 1 for 15 hours. After the regeneration process, performance of a NH₃-SCR process is measured at 220° C. in the reaction fluid (not including SO₂) by using the catalysts of Embodiments 18 and 23 and Comparative Example 1.

NO_(X) conversions X_(NOX) of the catalysts in initial/deactivated (or poisoned)/regenerated states at 220° C. are shown in FIG. 18. All catalysts show similar NO_(X) conversions X_(NOX) (e.g., 74% to 77%) at 220° C. before being poisoned. It is shown that the NO_(X) conversions X_(NOX) of all catalysts are lowered after being poisoned but the NO_(X) conversions X_(NOX) of the poisoned catalysts of Embodiments 18 and 23 are higher than that of the poisoned catalyst of Comparative Example 1 by 2% to 8%. This means that the catalysts of Embodiments 18 and 23 of the present invention have increased resistances against SO₂/AS/ABS poisoning compared to the high-priced commercial catalyst (Comparative Example 1).

More meaningfully, after the low-temperature (260° C.) regeneration process, the NO_(X) conversions X_(NOX) of the catalysts of Embodiments 18 and 23 are almost the same as those before being poisoned. This means that the catalysts of Embodiments 18 and 23 of the present invention 1) may decompose AS/ABS at a low temperature, 2) may be regenerated at a low temperature, and 3) may be recovered to have initial NH₃-SCR activities when regenerated at a low temperature for a longer time. Meanwhile, after the low-temperature (260° C.) regeneration process, the NO_(X) conversion X_(NOX) of the commercial catalyst (Comparative Example 1) is almost the same as that after being poisoned. This means that the commercial catalyst (Comparative Example 1) 1) may not decompose AS/ABS at a low temperature and thus may not be regenerated at a low temperature. Experimental Example 12 shows that the catalysts of Embodiments 18 and 23 may replace the high-priced commercial catalyst of Comparative Example 1 and catalysts including desirable contents of active sites and promoters as proposed by the present invention may have increased life spans compared to commercial catalysts.

As described above, according to an embodiment of the present invention, a catalyst synthesized using 1) a metal vanadate A prepared based on binding between one selected from among Mn, Co, and Ni, and V, 2) a metal vanadate B prepared based on binding between one selected from among La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and V, or 3) a mixture of the metal vanadate A and the metal vanadate B, as an active site may have a high NO_(X) conversion and a high N₂ selectivity on the surface thereof in a wide NH₃-SCR temperature range. In addition, by 1) functionalizing the catalyst surface with SO_(Y) ²⁻ or 2) changing the amount of a metal/V precursor, an additional active site may be created, desirable interaction with NO_(X), NH₃, AS, and ABS may be induced, a redox character may be improved, a resistance against poisoning or hydro-thermal aging during catalytic reaction may be increased, and a capability of decomposing AS or ABS at a low temperature may be achieved. Based on the above advantages, performance and a life span of a heterogeneous catalyst for NH₃-SCR may be remarkably improved. However, the above-described effects are merely examples and the scope of the present invention is not limited thereto.

While the present invention has been particularly shown and described with reference to embodiments thereof, it will be understood by one of ordinary skill in the art that various changes in form and details may be made therein without departing from the scope of the present invention as defined by the following claims. 

What is claimed is:
 1. A nitrogen oxide (NO_(X)) reduction catalyst comprising: a first active site comprising a metal vanadate expressed by Chemical Formula 1 (M₁)_(X)V₂O_(X+5) where M₁ denotes one selected from among manganese (Mn), cobalt (Co), and nickel (Ni), and X denotes a real number having a value between 1 and 3; a second active site comprising a metal vanadate expressed by Chemical Formula 2 (M₂)_(Y)VO₄ where M₂ denotes one selected from among lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu), and Y denotes a real number having a value between 0.5 and 1.5; and a support for loading both of the first and second active sites thereon, wherein the support comprises oxide of at least one selected from the group consisting of nitrogen (N), phosphorus (P), sulfur (S), arsenic (As), selenium (Se), antimony (Sb), tellurium (Te), polonium (Po), moscovium (Mc), livermorium (Lv), and any combination thereof, as a promoter.
 2. The NO_(X) reduction catalyst of claim 1, wherein the promoter has a composition range of 1 wt % to 5 wt % based on the total weight of the support.
 3. The NO_(X) reduction catalyst of claim 1, wherein the promoter has a composition range of 0.5 wt % to 3 wt % based on a total weight of the NO_(X) reduction catalyst.
 4. The NO_(X) reduction catalyst of claim 1, wherein at least a part of a surface of the NO_(X) reduction catalyst is sulfated.
 5. The NO_(X) reduction catalyst of claim 1, wherein at least a part of a surface of the NO_(X) reduction catalyst is sulfated and functionalized with SO_(Y) ²⁻. 